Atypical Myopathy (Sycamore Myopathy)

Equine Atypical Myopathy (EAM) is a life threatening equine disease that interferes with the uptake and use of glucose in the muscles. It is extremely serious with a mortality rate of some 75%, early veterinary care is essential for a horse to have a chance of survival. Early veterinary intervention and care is essential for a horse to have a chance of survival from Equine Atypical Myopathy.

What causes Equine Atypical Myopathy in horses?

Recent research, shows Equine Atypical Myopathy is to be caused by the toxin hypoglycin A (HGA), which can be found in the seeds and seedlings of sycamore trees (Acer pseudoplatanus). There are more than 25 different species of Acer and not all possess the hypoglycin toxin and levels vary considerably between trees.

The disease is most common in the autumn when large numbers of sycamore seeds have fallen from the trees. Climatic conditions that increase seed fall such as storms and high winds should be considered as higher risk times. Another higher risk time is when lots of sycamore seedlings emerge together in the spring.

What are the symptoms of Equine Atypical Myopathy?

The Hypoglycin A toxin affects the horse’s body by slowing or preventing energy from being produced within muscle cells, including the heart and so symptoms include general weakness and the horse may even struggle to stand and walk. Some horses are much more susceptible than others; some of whom may even have a high concentration of HGA in their blood and show few or no clinical signs.

Summary of signs of atypical myopathy in horses:

  • Colic like symptoms – although horses usually still have an appetite in contrast to those with gastro-intestinal related colic
  • Muscle tremors
  • Laboured breathing
  • Struggling to walk or stand
  • Low-hanging head
  • Fast or irregular heart rate
  • Recumbency

Actions to help reduce the risk of Equine Atypical Myopathy

  • Call a vet immediately if you suspect your horse is suffering from Atypical Myopathy. Early recognition and treatment is essential to maximise your horse’s chance of survival
  • Check your fields and neighbouring fields, woodland and hedgerows for sycamore trees – seeds can carry some distance (200 yards) in windy conditions for example, so you need to be aware of what is growing in proximity to your fields.
  • Be aware that a field without sycamore trees can still contain seeds spread by high winds or flood waters.
  • Supplementary feeding in the field to minimise the risk of horses being tempted to ingest seeds (such as supplementary forage or a bucket of suitable forage replacer)
  • If you can not remove the sycamore trees or seedlings, fence off affected areas.
  • Remove sycamore seeds and leaves where possible.
  • Limit grass turnout in affected fields and offer supplementary feed in the field to minimise the risk of horses being tempted to ingest sycamore seeds.
  • Where a case is suspected, remove field mates from the pasture and blood test to check if they could also be developing the atypical myopathy.
  • Test for the presence of HGA in your horse’s pasture.

Feeding advice for horses with suspected atypical myopathy

  • Avoid fasting
  • The diet should be rich in structural carbohydrate and low in lipids (contradictory to other muscle related conditions) Dengie Hi-Fi Senior would make an ideal inclusion in the ration, the blend of high temperature dried grass and alfalfa supplies a very digestible source of fibre but is low in oil. Dengie Pure Grass is a very soft form of grass that can be used as a forage replacer and contains no added oil. It is normally a very palatable feed making it ideal to temp a sick horse.
  • Allow free access to Fibre Feeds such as grass, hay and alfalfa
  • Avoid feeding excess grain
  • B vitamins and antioxidants, such as vitamin E have been shown to be beneficial to help support muscle function.
  • Colic and choke have been associated with Equine Atypical Myopathy, soaked fibre feeds such as Dengie Alfa-Beet may be beneficial in these scenarios

If you would like any further advice and guidance on Equine Atypical Myopathy visit the Royal Veterinary College.

If you would like advice on your horse’s ration or choosing a suitable forage replacer please contact our feedline on 01621 841188 to speak to our team of nutritionists or alternatively fill in our Feed Advice form.